Apparatus for delivery of gas to patients

ABSTRACT

Apparatus (10) is provided for controlled delivery of gas to a patient. The apparatus is particularly useful for delivery of anaesthetic gases in circumstances where the patient is conscious and able to receive gas upon demand and also where ventilation is poor. The apparatus (10) includes an outlet duct (40) for conveying gas from a gas supply (25) to the patient. A waste gas inlet duct (60) is also provided for receiving gas exhaled by the patient. This is connectable to a suction source (at 35) for scavenging the waste gas. The waste gas inlet duct (60) is arranged so that it can receive gas exhaled by the patient with the outlet duct (via a valve or other diverting means (80)) and around the outlet duct (as guided by shroud (70)).

The present invention relates to apparatus for use in delivery of gasesto patients. The invention finds particular, but not exclusive, use inrelation to delivery of anaesthetic gases.

BACKGROUND OF THE INVENTION

There is increasing concern regarding repeated exposure of medical staffto agents which are potentially harmful to them in the long term. Suchagents include anaesthetic gases.

Apparatus exists for controlled supply of anaesthetic gases to apatient. Example apparatus currently available incorporates a face mask.The mask is typically constructed to overlie the patient's face aroundthe mouth and to form a tight seal between the mask and face. Otherexample apparatus includes a rigid mouthpiece on the outlet of the gassupply tube. Rather than overlying the patient's face as in the previousexample, the mouthpiece is retained in the patient's mouth.

Apparatus currently available is capable of supplying gas to a patienton demand, that is only as and when required by the patient. In thisrespect, the apparatus often includes regulator means which incorporatea valve. In use, as a patient inhales, they apply a negative pressure tothe gas supply apparatus. When this happens, a valve in the regulator isopened to permit supply of gas to the patient. In the absence of thisnegative pressure, the valve is closed and so prevents inadvertentrelease of gas other than when required by the patient. Likewise, whenthe patient closes their mouth or exhales, the valve is also closed tocut off the supply of gas. In this way, the gas is supplied to thepatient only as and when required by them.

Such systems are particularly useful in cases where the patient isessentially in control of the mouthpiece or mask. This situationtypically arises in labour or maternity wards. In those circumstances,so-called "gas and air" (a mixture of equal quantities of nitrous oxideand oxygen) is available for supply to the mother-to-be (or patient).

During labour, the patient is typically given a gas supply apparatushaving a mouthpiece or mask, such as described above, and is free todraw from it as and when required. For times when the patient does notrequire the gas, they may remove the mask or mouthpiece from their face.When this is done, the regulator recognises that there is a lack ofdemand and the relevant valve is closed to shut off supply of gas to themask or mouthpiece, as appropriate.

In this way, existing apparatus limits the extent to which anaestheticgas is leaked into the patient's surroundings. It will be appreciatedthat gas leaked in this way is exposed to medical staff attending thebirth. In the long term, this is likely to be detrimental to the healthof the medical staff.

However, additional problems also arise in that, even though it ispossible to cut off the supply to the patient, gas is neverthelessexhaled by the patient. Thus, when a patient exhales, this supplies awaste mixture of carbon dioxide and some anaesthetic gas into thesurrounding atmosphere. As a result, any medical staff in attendance arealso exposed to undesirable amounts of waste anaesthetic gas.

This is a particular problem in labour wards which have inadequateventilation, which reduces likelihood of the exhaled gas being exhaustedfrom the ward.

In the light of concern for health and safety of employees in theworkplace, there is a desire to reduce the extent to which medical staffare exposed to waste anaesthetic gases. Indeed, it is expected thatstatutory maximum limits will be introduced. For example, a possiblemaximum limit could be 100 parts/million for nitrous oxide as an 8 hourtime weighted average.

SUMMARY OF THE INVENTION

The present invention seeks to alleviate at least some of theaforementioned problems.

Accordingly, in one broad aspect the present invention providesapparatus for controlled delivery of gas to a patient, which apparatusis connectable to a means for supplying gas and a means for withdrawingwaste gas, the apparatus comprising an outlet duct for conveying gasfrom the gas supply to the patient and a waste gas inlet duct capable ofreceiving gas exhaled by the patient into and around said outlet duct.

Thus the present apparatus is distinguished from many prior systems inthat it can be used to scavenge waste gas exhaled by the patient intothe outlet duct and gas exhaled and thereby released around the outletduct. This is a characterising feature of the present invention.

In preferred applications of the present invention, the gas supply is ofso-called gas and air, commercially available under the registered trademark ENTONOX.

Suitably, an outlet duct extends laterally from a gas supply line,typically to provide a mouthpiece for the apparatus. Preferably, theoutlet duct includes a mouthpiece which comprises a rigid tube memberflattened at its free end so as to be generally elliptical incross-section.

The inlet duct is connectable to a suction source or other means forwithdrawing waste gas from the apparatus. The apparatus convenientlyincludes a gas supply line and a means for releasably coupling the gassupply line to a gas source and a waste gas exhaust line and means forreleasably coupling the exhaust line to a suction source. Generally suchcoupling means will not be interchangeable to ensure that the apparatusis appropriately linked to the suction source and gas supply.Alternatively, or in addition the coupling means may have some form ofindicia to distinguish them.

Preferably, the apparatus includes means for diverting gas exhaled intothe outlet duct to the waste gas inlet duct. Passage of the divertedwaste gas is assisted by the suction source, as described above.Preferably, the diverting means take the form of a valve, arranged to beopenable under the influence of waste gas exhaled by a patient therebyto permit the waste gas to communicate with the waste inlet duct. Inthis regard the gas is typically supplied to the patient at a pressurewhich is not sufficient to actuate the diverting means.

Suitably, such a valve includes an opening provided in a wall of a gassupply line and a moveable closure member for closing the opening, whichclosure member is biased towards a closed position and arranged suchthat pressure of exhaled waste gas is sufficient to displace the movableclosure member from the opening.

Preferably, the waste gas inlet duct is arranged so that, in use, it ispresented at a level below that of the valve opening. Suitably, thewaste inlet duct is also arranged so that, in use, it is spaced from thepatient.

In preferred embodiments, the apparatus incorporates a shroud capable ofoverlying at least part of a patient's face and to provide a chamber forwaste gas exhaled by the patient. Preferably, the chamber accommodatesat least the patient's nose. In such preferred embodiments, the shroudtakes the form of a mask, adapted to overlie at least the nose and mouthof a patient. Preferably, the shroud is constructed of a generallytransparent material. In preferred embodiments, the mask is of aform-sustaining material which has some flexibility. This reduceslikelihood of the shroud being damaged, or of it injuring a patient, ifthe patient were to inadvertently lie on it.

In preferred embodiments, the shroud is arranged such that its perimeterdoes not closely abut the patient. In particularly preferredembodiments, the outlet duct of the apparatus is arranged to extendbeyond the perimeter of the shroud such that, in use, the shroud doesnot abut the patient.

In another broad aspect, the invention concerns a system for deliveringgas to a patient and for withdrawing waste gas and which includesapparatus as described above.

Embodiments of the present invention will now be described further, byway of example, with reference to the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of example apparatus;

FIG. 2 is a front elevational view of the apparatus of FIG. 1; and

FIG. 3 is a schematic diagram illustrating a waste anaesthetic gasscavenging system which incorporates the apparatus as shown in FIGS. 1and 2.

DETAILED DESCRIPTION OF THE INVENTION

The illustrated apparatus 10 includes a gas supply line 20 and a wastegas exhaust line 30. The gas supply line 20 may be coupled to a gassupply (not illustrated) at 25. The waste gas exhaust line 30 may becoupled to a waste gas scavenging system which includes a suction source(not illustrated) at 35. An example of gas which may be delivered usingthe present apparatus is available under the registered trade markENTONOX. As discussed above, this is so-called gas and air. It is amixture of nitrous oxide and oxygen. Of course, the apparatus may beused for supply of other gases.

The gas supply line 20 and gas exhaust line 30 are accommodated in acasing 28. The casing has surface formations 29 to facilitate grip onthe apparatus 10 by the patient.

The apparatus 10 includes an outlet duct 40, inlet duct 60 and shroud70.

In more detail, the outlet duct 40 comprises a mouthpiece 48 whichcommunicates with the free end of a gas supply line 20 via angled tubing45. In this way, the mouthpiece 48 extends laterally from the gas supplyline 20. The mouthpiece 48 is flattened at its free end 49 and is of anappropriate size and shape so that it may be comfortably accommodated ina patient's mouth. Such mouthpieces are conventional.

The inlet duct 60 comprises a channel 62 having an inclined open end 63.

The angled tubing 45 of the outlet duct 40 includes means for divertinggas from the outlet duct 40 to the waste inlet duct 60. The divertingmeans are indicated generally at 80. In more detail, the angled tubing45 includes an opening 88. The opening 88 defines a valve seat. Amovable closure member 89 is mounted on the seat 88. The closure member89 is biased into a closed position by biasing means 50 in the form of acompression spring. The closure member 89 is accommodated in a generallycylindrical housing 51 having an outlet port 52 in communication withopening 88.

The shroud 70 is made of a semi-flexible material, such as a plastic.The shroud is constructed to be generally transparent. The shroud has agenerally circular perimeter 71 and may be arranged alongside apatient's face so as to define a chamber 72. This is illustrated in FIG.1.

The base of the shroud 70 is apertured to permit passage of gas supplyline 20 and gas exhaust line 30 therethrough. The shroud 70 is typicallymounted on the lines 20, 30 in such a way as to permit slight slidingadjustment of the shroud 70 with respect to the lines so as to define anappropriate spacing between the shroud 70 and the grip formations 29suitable for the user.

The apparatus 10 is constructed so that the free end 49 of mouthpiece 48extends beyond the perimeter 71 of the shroud 70.

The apparatus may be employed as follows. The free end 49 of mouthpiece48 is accommodated in a patient's mouth. As and when a patient inhalesand draws on the mouthpiece 48, gas is supplied along the supply line 20to the mouthpiece 48. The gas is supplied upon demand, using regulatormeans as described above. As with conventional apparatus, when thepatient releases their grip on the mouthpiece 48, or perhaps removes itfrom their mouth, the supply of gas to line 20 is cut off.

The present apparatus differs from existing apparatus in the way inwhich it scavenges waste gas exhaled from a patient.

In order to scavenge waste gas, a suction source coupled at 35 to thewaste gas exhaust line 30 is actuated. When the patient exhales throughtheir nose, waste gas is supplied into chamber 72 defined by shroud 70.The suction source on line 30 draws the waste gas to inlet duct 60. Thewaste gas is subsequently drawn along line 30. The gas may then bechannelled to a remote location for disposal, as illustrated in FIG. 3,for example. Alternatively, the apparatus may be provided with its owndedicated suction source.

When the patient exhales through their mouth, some waste gas will bedelivered into chamber 72 around the external periphery of mouthpiece48. This waste gas may be drawn to waste gas inlet 60 for disposal, inthe same way as waste gas exhaled from the nose.

However, when the patient exhales through their mouth rather than theirnose, some gas is also delivered into the outlet duct 40. This waste gaswill travel to angled tubing 45 and will contact valve seat 88. Thepressure of this waste gas is sufficient to displace the moveableclosure member 89 from its valve seat 88. This permits the waste gas toescape from opening 88 in the angled tubing 45 and to pass throughoutlet port 52 in valve housing 51. The waste gas at outlet port 52 isalso drawn towards the waste gas inlet 60 by the suction source. Thewaste gas is thus withdrawn from the locality of the patient fordisposal.

As illustrated in FIG. 3, the apparatus 10 may typically be incorporatedinto a system which includes a filter/silencer unit 100 and a monitorblock and vacuum gauge 200. The filter/silencer unit 200 is designed toprovide attenuation for the complete apparatus and filtration to preventany particulate matter or the like from entering the waste gas pipelinesystem.

The filter/silencer unit 100 conveniently comprises a head block 110 andmounting bracket attached thereto, to enable the unit 100 to bedetachably wall mounted. The unit 100 has an inlet port 120 to receivethe waste gas line from the apparatus 10. A clear cylindrical filterhousing 130 is detachably mounted to the head block 110. The housing 130incorporates a silencer and filter media (not illustrated). Examplefilter media is known in the trade as "Bondina". At the base of filterhousing 130, there is an outlet connection 140 to permit passage of gasto the vacuum gauge and monitor block 200.

The vacuum gauge and monitor block 200 is also adapted to be detachablymountable to a wall. The gauge is conveniently scaled from 0 to minus 10KPA.

The gauge reading is taken to ensure the system is functioning correctlywithin specified limits. Typically, the system will be functioning witha gauge reading of about 6 KPA Negative.

As shown in FIG. 3, the unit 200 has an inlet port 210 for receivingwaste gas from the filter/silencer unit 100. The system will typicallysupply Entonox (or other gas) at the same flow rate as conventionalapparatus. For example the system may suitably scavenge waste gas at arate which is within a range in the order of about 50 to 180 litres/minor whatever is appropriate to comply with local requirements.

The illustrated apparatus provides advantageous results. It isparticularly effective because it is capable of scavenging waste gasexhaled from both the nose and mouth of the patient. The advantages ofthe present apparatus will be illustrated by the following experimentalresults.

The following results show sample N₂ O exposure levels (ppm) usingconventional apparatus which employs as gas supply to a mouthpiece suchas used in the present invention

    ______________________________________    MIDWIFE      PARTNER   BACKGROUND    ______________________________________    1488 (419)   4060 (1142)                           3615 (1017)    997 (398)    --        1015 (398)    666 (486)    1854 (1359)                           1707 (1245)    ______________________________________

The figures in brackets denote 8 hour time weighted averages. "Partner"refers to a person attending the birth with the mother-to-be.Experiments under comparable conditions and using apparatus of thepresent invention have provided exposure levels of as low as from 65(28)to 86(22) for an anaesthetist at respective background levels of from113 (48) to 185 (46).

Suitably the mouthpiece 48 is releasable from the angled tubing 45 so asto permit it to be disposed of. Typically the angled tubing 45 will alsobe releasable from the gas supply line 20 so as to permit the shroud 70to be removed (by sliding it out of engagement with lines 20, 30) forcleaning or for replacement if damaged.

Thus, as shown in FIG. 3 the illustrated apparatus may be coupled to anexisting scavenging system for withdrawal of waste gas. In which casethe filter/silencer unit, monitor block and vacuum gauge are employed toprotect the apparatus from demands made by other users of the scavengingsystem. Alternatively the apparatus may be provided with its owndedicated suction source for withdrawing exhaled gas. In cases where theapparatus is employed with a dedicated suction source, thefilter/silencer unit, monitor block and vacuum gauge described above maybe dispensed with.

The present invention has particular application in circumstances wheregases are supplied to patients in locations which are poorly ventilatedand thus where there is inadequate withdrawal of waste gas. This couldbe in hospital wards, for example, or in other closed environments suchas ambulances. It would, of course, also have application in reasonablywell ventilated areas where problems with localised high concentrationof gases may arise.

Of course, various modifications may be made to the illustratedembodiment. For example, the valve means or other arrangement includedin the diverting means may take various forms. Also, any such valvecould be presented in a side wall of a gas supply line, so as to befacing the free end of the mouthpiece, rather than alongside themouthpiece as illustrated. Also if desired an additional valve could beprovided in the gas supply line near its junction with the means fordiverting gas exhaled into the outlet duct to the waste gas inlet duct.

We claim:
 1. Apparatus for controlled delivery of gas to a patient whichapparatus is operatively connectable to a gas supply and to means forwithdrawing waste gas, the apparatus comprising an outlet duct forconveying gas from the gas supply to the patient, a chamber disposedaround said outlet duct for receiving gas exhausted by said patient, anda waste gas inlet duct having an opening for receiving gas exhaled bysaid patient from outside of said outlet duct and from inside of saidoutlet duct; characterized by further including means for divertingexhaled gas from the outlet duct to the waste gas inlet duct, wherebygas exhaled by said patient into said outlet duct is also received insaid waste gas inlet duct.
 2. Apparatus according to claim 1 whichincludes a gas supply line and means for releasably coupling the gassupply line to a gas source and a waste gas exhaust line and means forreleasably coupling the exhaust line to a suction source.
 3. Apparatusaccording to claim 2 wherein the gas supply outlet duct extendslaterally from the gas supply line for the apparatus.
 4. Apparatusaccording to claim 1 wherein the gas supply outlet duct includes areleasable mouthpiece for locating in a patient's mouth.
 5. Apparatusaccording to claim 1 wherein the means for diverting exhaled waste gasincludes valve means arranged to be openable under the influence ofpressure of waste gas exhaled by a patient into the gas supply outletduct so as to permit the gas supply outlet duct to communicate with thewaste gas inlet duct.
 6. Apparatus according to claim 5 wherein thevalve means includes an opening in a gas supply line, a movable closuremember for selectively closing the opening, and means for biasing themember to a closed position, the closure member being arranged to bedisplaceable once pressure of exhaled gas at the gas supply outlet ductreaches a predetermined level.
 7. Apparatus according to claim 1 whereinthe waste gas inlet duct is arranged at a level below that of the meansfor diverting exhaled waste gas from the gas supply outlet duct. 8.Apparatus according to claim 2 wherein the gas supply line and/or thewaste gas exhaust line have external surface formations to assist fingergrip by a patient.
 9. Apparatus according to claim 1 which includes ashroud capable of overlying at least part of a patient's face in use soas to provide the chamber for exhaled waste gas.
 10. Apparatus accordingto claim 9 wherein the shroud is constructed to overlie at least thenose and mouth of a patient.
 11. Apparatus according to claim 9 whereinthe shroud is at least partly transparent.
 12. Apparatus according toclaim 9 wherein the waste gas inlet duct is located within the chamberdefined by the shroud and the gas supply outlet duct extends outside ofthe chamber and beyond the perimeter of the shroud.
 13. Apparatusaccording to claim 9 wherein the shroud is mounted in the apparatus soas to permit adjustment of its position relative to the gas supplyoutlet duct.
 14. Apparatus according to claim 9 wherein the shroud isreleasable for maintenance.
 15. Apparatus according to claim 1 furthercomprising a gas supply.
 16. Apparatus according to claim 1 furthercomprising a means for withdrawing waste gas exhaled by the patient. 17.Apparatus for controlled delivery of gas to a patient which apparatus isoperatively connectable to a gas supply and to means for withdrawingwaste gas, the apparatus comprising:an outlet duct for conveying gasfrom the gas supply to the patient; a shroud defining a chamber disposedaround said outlet duct for receiving gas exhausted by the patient, theshroud being adapted to be placed over the patient's nose and mouth; awaste gas inlet duct which is arranged to receive gas that is exhaled bythe patient into said chamber directly from the chamber such that thegas exhaled into the chamber by-passes the outlet duct; and means fordiverting exhaled gas from the outlet duct and to the waste gas inletduct such that gas which is exhaled by the patient directly into theoutlet duct is received in said waste gas inlet duct through thediverting means.